Medication reconciliation is a focus of efforts to engage patients in safety programs, as prior studies have shown that patients are an important source of information in the medication reconciliation process. This cohort study conducted in an urban emergency department compared the accuracy of patient-reported medication lists with a "gold standard" list compiled from pharmacies and found that only 36.3% of patients were able to provide a medication list that exactly matched the pharmacy list. Errors of omission (failure to include a prescribed medication) were the most common, and a significant proportion of omitted medications were considered high-risk. A medication error caused in part by a discrepancy between patient-reported medications and the medical record is discussed in this AHRQ WebM&M commentary.